Which merc best for blizz mf sorc?

DEFIANCE ?

I always have used defiance but i recently been using the merc that gives life back.. doesnt seem to have any benefit

Does a defiance merc at least stay alive longer?

You can either get a insight weapon on him and have him using prayer, or make him into a damage dealer and have might equipped.
Defiance isn't that bad as well considering your defense will also improve vs monsters that tend to benefit from strong physical attacks that usually have hit checks.

Most people will usually turn to the damage dealer version with might.

Might Merc in my opinion. Holy Freeze is good too, but honestly if you're using Chilling or Frozen Armor yourself, you don't need it. Depends on skill set. Might Merc really makes an early gear Sorc viable in Hell, since your Merc can still pack a punch with trash gear.

You could try an A5 Merc too, but I'm running a non eth Insight in a self found GPA with Treachery and Tal Helm and it kills.